Wireless communication system, and apparatus and method for wireless communication

ABSTRACT

An embodiment of the invention provides a wireless communication system for carrying out a spatial multiplexing communication between a transmitter, and a receiver, the system including: a channel information matrix acquiring section for acquiring a channel information matrix; a weighting factor matrix arithmetically operating section for obtaining a weighting factor matrix based on the channel information matrix thus acquired; a normalizing section for executing processing for normalizing the weighting factor matrix; a detecting section for detecting whether there is presence or absence of an abnormality in the processing; a weighting processing section for executing weighting processing based on the weighting factor matrix for each of transmission signals transmitted from the transmitter in accordance with a detection result obtained from the detecting section; and a transmitting section for transmitting the transmission signals for which the weighting processing section executes the weighting processing from the transmitter to the receiver.

CROSS REFERENCES TO RELATED APPLICATIONS

The subject matter of application Ser. No. 11/974,299 is incorporatedherein by reference. The present application is a Divisional of U.S.application Ser. No. 11/974,299, filed Oct. 12, 2007, which claimspriority to Japanese Patent Application JP 2006-302792 filed in theJapanese Patent Office on Nov. 8, 2006, the entire contents of whichbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system withwhich communications are mutually made among a plurality of wirelessstations as in a wireless local area network (LAN), and an apparatus anda method for a wireless communication. More particularly, the inventionrelates to a wireless communication system with which high speed datatransmission is realized through multiplexing for a transmission line,and an apparatus and a method for wireless communication.

More specifically, the present invention relates to a wirelesscommunication system with which high speed transmission is realizedthrough a multiple input multiple output (MIMO) communication utilizingspatial multiplexing between a transmitter having a plurality ofantennas and a receiver having a plurality of antennas, and an apparatusand a method for a wireless communication. More specifically, theinvention relates to a wireless communication system with which signalsare multiplexed and the multiplexed signals are transmitted withoutbeing influenced by crosstalk at all by using a singular valuedecomposition (SVD)-MIMO communication system utilizing the SVD of achannel information matrix H, and an apparatus and a method for awireless communication.

2. Description of the Related Art

A wireless network attracts attention as a system for release fromwirings in the traditional wired communication system. The Institute ofElectrical and Electronics Engineers (IEEE) 802.11 and IEEE802.15 can begiven as the standards for the wireless network.

A modulation system with which a communication speed of up to 54 Mbps isattained is supported based on the standard of IEEE802.11a/g. However,in recent years, the wireless LAN standards of the next generation withwhich the higher bit rate can be realized have been desired.

A multi-input multi-output (MIMO) communication attracts attention asone of the techniques for realizing the speeding up of the wirelesscommunication. The MIMO communication is a communication system whichincludes a plurality of antenna elements on each of a sender side and areceiver side, and which realizes a stream obtained through spatialmultiplexing. According to the MIMO communication system, a transmissioncapacity can be increased in correspondence to the number of antennaswithout increasing a frequency band, thereby attaining the increase incommunication speed. In addition, utilization of the spatialmultiplexing results in the excellent frequency use efficiency beingobtained. The MIMO communication system is a communication systemutilizing the channel characteristics, and thus is different from asimple transmitting and receiving adaptive array.

For example, IEEE802.11n as an extended standard of IEEE802.11a/g adoptsan OFDM_MIMO system using an OFDM in primary modulation. Thus, thecommunication becomes possible at the transmission speed of 100 to 600Mbps. An industry organization called Enhanced Wireless Consortium (EWC)which was organized on October, 2005 currently performs the developmentand promotion conforming to the IEEE802.11n specification with the MIMOas base.

The MIMO communication system is constructed as follows. That is to say,a channel information matrix H between a sender side and a receiver sideis acquired by utilizing some kind of method. Moreover, the transmissionsignals spatially multiplexed in a phase of the transmission by usingthe channel information matrix H are spatially separated into aplurality of original streams in accordance with a predeterminedalgorithm.

The channel information matrix H is obtained as follows. That is to say,normally, the known training sequence is transmitted between a senderside and a receiver side through pairs of antennas. A channeltransmission functions is estimated from a difference between theactually received signal and the known sequence. Also, the transmissionfunctions for a combination of the sender side antennas and the receiverside antennas are arranged in the form of a matrix. When the number ofsender side antennas is M, and the number of receiver side antennas isN, the channel information matrix becomes a matrix of N×M (row×column).

In addition, the method of spatially separating the received signals isroughly classified into two types. That is to say, one type is an openloop type in which the receiver carries out independently the spatialseparation in accordance with the channel information matrix H. Also,the other type is a closed loop type in which the suitable beamformation is carried out for the receiver on the transmitter side aswell by performing the sender side antenna weighting in accordance withthe channel information matrix, thereby making an ideal spatialorthogonal channel. A singular value decomposition (SVD)-MIMOcommunication system utilizing the SVD of the channel information matrixH is known as one of the ideal forms of the closed loop type MIMOtransmission.

FIG. 7 conceptually shows the SVD-MIMO communication system. In theSVD-MIMO communication system, the channel information matrix H havingthe channel information (transmission functions) corresponding to thepairs of antennas as elements is subjected to the singular valuedecomposition, thereby obtaining UDV^(H). Also, V is given as the senderside antenna weighting factor matrix, and U^(H) is given as the receiverside antenna weighting factor matrix. Here, a superior H representscomplex conjugate transpose.

Here, D represents a diagonal matrix having square roots of eigenvaluesλ_(i) of a covariance matrix A of the channel information matrix H asdiagonal elements (a suffix i means an i-th spatial stream). Also, theeigenvalues λ_(i) correspond to qualities of the corresponding spatialstreams, respectively. The singular values λ_(i) are arranged in theorder of decreasing the value of the diagonal element of the diagonalmatrix D, and a power ratio distribution corresponding to thecommunication quality represented by the magnitude of the singularvalue, and an allocation of the modulation system are carried out forthe streams. As a result, it is possible to realize a plurality oftheoretically independent transmission lines for which the spatialorthogonal multiplexing is carried out. Thus, the receiver side can takeout a plurality of original signal sequences without being influenced bythe crosstalk at all, and the highest performance can be theoreticallyattained.

In the example shown in FIG. 7, the transmitter includes M transmissionantennas. Thus, the transmitter distributes the transmission data to theK transmission streams, multiplexes the transmission data through thespatial/time encoding, and distributes the multiplexed transmission datato the transmission antennas, respectively, thereby transmitting themultiplexed transmission data through the respective channels. Atransmission signal x′ at this time is expressed in the form of a vectorof M×1. On the other hand, the receiver includes the N receptionantennas. Thus, the receiver subjects a received signal y′ expressed inthe form of a vector of N×1 to the spatial/time decoding, therebyobtaining the received data composed of the K reception streams withoutthe crosstalk among the streams. The channel information matrix in thiscase is expressed in the form of a matrix H of N×M. Also, the spatialstreams having only the number which is less one (MIN[M, N]) of thenumber of sender side antennas, and the number of receiver side antennasare ideally formed.

An element h_(ij) of the channel information matrix H is thetransmission function from the j-th transmission antenna to the i-threception antenna (where i is a positive integral number of 1 to N, andj is a positive integral number of 1 to M). Also, the received signalvector y′ is expressed by the following expression (1) in which a noisevector n is added to the product of the transmission signal vector andthe channel information matrix.y′=Hx′+n  (1)

When being subjected to the singular value decomposition in the manneras described above, the channel information matrix H is expressed by thefollowing expression (2):H=UDV ^(H)  (2)

Here, the sender side antenna weighting factor matrix V, and thereceiver side antenna weighting factor matrix U^(H) are unitary matriceswhich meet the following expressions (3) and (4), respectively:U ^(H) U=I  (3)V ^(H) V=I  (4)

Where I represents a unit matrix.

That is to say, a matrix in which the normalized eigenvectors of HH^(H)are arranged is the receiver side antenna weighting factor matrix U^(H).Also, a matrix in which the normalized eigenvectors of H^(H)H arearranged is the sender side antenna weighting factor matrix V. Inaddition, D is the diagonal matrix, and has square roots of theeigenvalues λ of H^(H)H or HH^(H) as the diagonal components. In otherwords, when smaller one of the number, M, of sender side antennas, andthe number, N, of receiver side antennas is L(=min (M, N)), the diagonalmatrix D becomes a square matrix of L×L as expressed by the followingexpression (5):

$\begin{matrix}{D = \begin{bmatrix}\sqrt{\lambda_{1}} & 0 & \ldots & 0 \\0 & \sqrt{\lambda_{2}} & \ldots & 0 \\\vdots & \vdots & \ddots & \vdots \\0 & 0 & \ldots & \sqrt{\lambda_{L}}\end{bmatrix}} & (5)\end{matrix}$

In the system shown in FIG. 7, the transmitter carries out the weightingtransmission by using the antenna weighting factor matrix V in the phaseof the transmission. On the other hand, the receiver carries out theweighting reception by using U^(H) as the antenna weighting factormatrix in the phase of the reception. Therefore, since each of thematrices U and V is the unitary matrix (U is the matrix of N×L, and V isthe matrix of M×L), the received signal y is expressed by the followingexpression (6):

$\begin{matrix}\begin{matrix}{y = {U^{H}y^{\prime}}} \\{= {U^{H}\left( {{Hx}^{\prime} + n} \right)}} \\{= {U^{H}\left( {{HVx} + n} \right)}} \\{= {{{U^{H}\left( {UDV}^{H} \right)}{Vx}} + {U^{H}n}}} \\{= {{\left( {U^{H}U} \right){D\left( {V^{H}V} \right)}x} + {U^{H}n}}} \\{= {{IDIx} + {U^{H}n}}} \\{= {{Dx} + {U^{H}n}}}\end{matrix} & (6)\end{matrix}$

Here, the received signal y and the transmission signal x are notexpressed in the form of vectors depending on the number of sender sideantennas, and the number of receiver side antennas, respectively, butare expressed in the form of (L×1) vectors, respectively. Thetransmission signal for each stream can be received without beinginfluenced by the crosstalk at all because D is the diagonal matrix.Also, since the diagonal elements of the matrix D become the squareroots of the eigenvalues λ_(i), the electric power of each of thereceived signals is proportional to λ_(i). In addition, for the noisecomponent n, each of the columns of U has the eigenvectors each having anorm normalized to 1. Hence, U^(H)n changes no noise electric power.With respect to the size, U^(H)n becomes a (L×1) vector, and y and xhave the same size.

As described above, in the SVD-MIMO transmission, a plurality ofindependent and logical paths each of which is free from the crosstalkcan be obtained in spite of the same frequency and the same time. Thatis to say, a plurality of data can be transmitted through the wirelesscommunication by using the same frequency at the same time. As a result,it is possible to realize the improvement in the transmission speed.

As have been described above, the antenna weighting method in thetransmitter, especially, the weighting method for the SVD-MIMOtransmission (eigenmode transmission) can be expressed in the form of amathematical expression. It is necessary for the normal actual equipmentto execute the processing in real time by using an arithmeticallyoperating circuit which is structured with the realistic circuit scale.For this reason, the integer arithmetic operation is carried out for thecalculation for obtaining the weighting factor matrix from the channelinformation matrix H. Unlike the real number arithmetic operation, theinteger arithmetic operation causes a problem such as an increase inarithmetic operation error, an overflow, an underflow or the like due toan influence of a word length limitation. As a result, there is the highpossibility that the row norm of the weighting factor matrix largelyvaries.

On the other hand, an upper limit is generally set in the transmissionoutput of the wireless transmitter from the Radio Law control or thelike. Here, normally, the transmission is carried out with the output aslarge as possible in the range of not exceeding the upper limit becausethe transmission output is connected directly with a communicationdistance. In the transmitter as well which carries out the weightingtransmission described above, the matrix V having the row normnormalized to 1 is used as the weighting factor matrix, therebypreventing the transmission output from fluctuating for any weightingfactor matrix (that is, thereby preventing the transmission output fromexceeding the upper limit).

However, in the case where the arithmetic error, the overflow or thelike accompanying the integer arithmetic operation or the like asdescribed above occurs in the process for arithmetically operating theweighting factor matrix, it is possible that the weighting factor matrixbecomes the unexpected value. Thus, it is the possibility that thetransmitter multiples the transmission signal by the transmissionweighting factor matrix having the unexpectedly large value, so that theoutput of the resulting signal exceeds the upper limit of thetransmission output, thereby running foul of the Radio Law control.

The technique as described above, for example, is disclosed in JapanesePatent Laid-Open No. 2005-160030.

SUMMARY OF THE INVENTION

In the light of the foregoing, it is desirable to provide an excellentwireless communication system which is capable of realizing high-speeddata transmission through an MIMO communication utilizing space-divisionmultiplexing between a transmitter having a plurality of antennas and areceiver having a plurality of antennas, and an apparatus and a methodfor a wireless communication.

It is also desirable to provide an excellent wireless communicationsystem which is capable of multiplexing and transmitting signals withoutbeing influenced by the crosstalk at all by using an SVD-MIMOcommunication system utilizing singular value decomposition of a channelinformation matrix H, and an apparatus and a method for wirelesscommunication.

It is further desirable to provide an excellent wireless communicationsystem which is capable of realizing an improvement in a transmissionspeed through SVD-MIMO transmission by calculating a weighting factormatrix by using an integer arithmetically operating circuit limited in aword length in a transmitter, and an apparatus and a method for wirelesscommunication.

It is still further desirable to provide an excellent wirelesscommunication system which is capable of realizing an improvement in atransmission speed through SVD-MIMO transmission by reducing thepossibility that a transmission electric power exceeds an upper limitthrough the suppression of a fluctuation in row norm of a weightingfactor matrix accompanying an arithmetic operation error or an overflowwhen the weighting factor matrix is obtained by using an integerarithmetically operating circuit limited in a word length in atransmitter, and an apparatus and a method for wireless communication.

According to an embodiment of the present invention, there is provided awireless communication system for carrying out a spatial multiplexingcommunication between a transmitter having a plurality of antennas, anda receiver having a plurality of antennas, the wireless communicationsystem including:

channel information matrix acquiring means for acquiring a channelinformation matrix having transmission functions of the pairs ofantennas between the sender side and the receiver side as elements;

weighting factor matrix arithmetically operating means for obtaining aweighting factor matrix based on the channel information matrix thusacquired;

normalizing means for executing processing for normalizing the weightingfactor matrix;

detecting means for detecting whether there is presence or absence of anabnormality in the processing executed by the weighting factor matrixarithmetically operating means or the normalizing means;

weighting processing means for executing weighting processing based onthe weighting factor matrix for each of transmission signals which aretransmitted from the transmitter in accordance with a detection resultobtained from the detecting means; and

transmitting means for transmitting the transmission signals for whichthe weighting processing means executes the weighting processing fromthe transmitter to the receiver.

However, “the system” stated herein means one in which a plurality ofapparatuses (or functional modules which realize specific functions,respectively) are logically assembled. Thus, it is especially no objectwhether or not the apparatuses or the functional modules are provided ina single chassis (and so forth on).

The MIMO communication is generally known as one of the techniques forrealizing the speeding up of the wireless communication. Especially,according to the SVD-MIMO communication system, the channel informationmatrix H having the channel information corresponding to the pairs ofantennas as the elements is subjected to the singular valuedecomposition, thereby obtaining UDV^(H). Thus, V is given as theantenna weighting factor matrix on the sender side, and U^(H) is givenas the antenna weighting factor matrix on the receiver side. As aresult, it is possible to realize a plurality of logically independenttransmission lines for which the orthogonal spatial multiplexing iscarried out. Also, a plurality of original signal sequences can be takenout on the receiver side without being influenced by the crosstalk atall, and thus the highest performance can be theoretically attained.

Here, the antenna weighting method for the transmitter is expressed inthe form of the mathematical expression. Also, it is necessary for thenormal actual equipment to execute the processing in real time by usingthe arithmetically operating circuit which is structured with therealistic circuit scale. For this reason, the integer arithmeticoperation is carried out for the calculation for obtaining the weightingfactor matrix from the channel information matrix H. Unlike the realnumber arithmetic operation, the integer arithmetic operation causes aproblem such as an increase in arithmetic operation error, an overflow,an underflow or the like due to an influence of a word lengthlimitation. As a result, there is the high possibility that the row normof the weighting factor matrix largely varies. For this reason, thoughthe matrix having the row norm normalized to 1 is used as the weightingfactor matrix, the unexpectedly large weighting factor matrix iscalculated due to the arithmetic operation error, the overflow or thelike which is generated in the phase of calculation of the weightingfactor matrix. As a result, there is the dangerousness that the outputof the transmission signal exceeds the upper limit controlled by theRadio Law or the like.

Thus, in the wireless communication system according to the embodimentof the present invention, the arithmetically operating means such as theweighting factor matrix arithmetically operating means and thenormalizing means are constituted by integer arithmetic operationmodules, respectively. In this case, however, the normalizing meansexecutes the processing for normalizing the weighting factor matrix inthe final stage of the processing for arithmetically operating theweighting factor matrix. As a result, the influence of the arithmeticerror or the overflow which is mixed into the weighting factor matrixarithmetic operation is reduced.

More specifically, the normalizing means carries out the normalizationfor the eigenvectors obtained from the eigenvalues of the covariancematrix of the channel information matrix in the weighting factor matrixarithmetically operating means. Or, the normalizing means carries outthe normalization for the transmission signal vectors after theweighting processing based on the weighting factor matrix is executed inthe weighting processing means.

When such normalizing means properly operates, the row norm of theoutput weighting factor matrix is usually held at a constant value.However, when the input signal to the weighting factor matrixarithmetically operating means becomes beyond the expected limit in theinteger arithmetic operation, it is possible that the arithmeticoperation error occurs, or the overflow or the underflow occurs in themiddle of the arithmetic operation. Therefore, the proper operation isnot necessarily guaranteed. In particular, there is the high possibilitythat the arithmetic operation error for a too large input or a too smallinput becomes large because the division is carried out based on thesquare-root of sum of squares in the normalizing processing.

Then, the detecting means detects that an input signal beyond apredetermined limit is input to the normalizing means, or that theoverflow or the underflow occurs in the middle of the arithmeticoperation for the normalization as an abnormality.

Also, when the detecting means detects the abnormality in thenormalizing processing, the weighting processing means outputs anotherweighted transmission signal having the row norm guaranteed thereforeinstead of weighting each of the transmission signals with a weightingfactor matrix arithmetically operated by the weighting factor matrixarithmetically operating means. As a result, it is possible to avoid thedangerousness that the transmission electric power exceeds the upperlimit set by the Radio Law control.

For example, the wireless communication system further includesnonvolatile memory means for previously storing therein one or moreweighting matrices each having the row norm guaranteed therefore, andwhen the detecting means detects the abnormality in the normalizingprocessing, the weighting processing means weights each of thetransmission signals by using a weighting factor matrix stored in thenonvolatile memory means. Thereby, it is possible to avoid thedangerousness that the transmission electric power exceeds the upperlimit set by the Radio Law control.

The weighting factor matrix having the row norm guaranteed therefore,for example, is a unit matrix, a rotation matrix having a suitableangle, a mirror matrix, a Walsh-Hadamard matrix, a matrix obtained bycombining these tow or more matrices with each other, or the like.

In addition, the nonvolatile memory means may store therein a pluralityof different weighting factor matrices, and when the detecting meansdetects the abnormality in the normalizing processing, the weightingprocessing means may suitably select optimal one from among theplurality of different weighting factor matrices stored in thenonvolatile memory means, and may weight each of the transmissionsignals.

More specifically, the nonvolatile memory means stores therein aplurality of rotation matrices having different angles, and when thedetecting means detects the abnormality in the normalizing processing,the weighting processing means selects one having an angle nearest theweighting factor matrix before execution of the normalizing processingfrom among the plurality of rotation matrices stored in the nonvolatilememory means, and weights each of the transmission signals.

In addition, the weighting factor matrix arithmetically operating meanscan produce a plurality set of eigenvectors based on eigenvaluesobtained from a covariance matrix of the channel information matrix thusacquired. Also, the weighting factor matrix arithmetically operatingmeans may select suitable one from among the plurality set ofeigenvectors, that is, a matrix having a small possibility that thearithmetic operation error finally occurs from among the plurality setof eigenvectors.

According to another embodiment of the present invention, there isprovided a wireless communication system for carrying out a spatialmultiplexing communication between a transmitter having a plurality ofantennas, and a receiver having a plurality of antennas, the wirelesscommunication system including:

channel information matrix acquiring means for acquiring a channelinformation matrix having transmission functions of the pairs ofantennas between the sender side and the receiver side as elements;

weighting factor matrix arithmetically operating means for obtaining aweighting factor matrix based on the channel information matrix thusacquired;

weighting processing means for executing weighting processing based onthe weighting factor matrix for transmission signals which aretransmitted from the transmitter;

transmission signal normalizing means for executing processing fornormalizing each of the transmission signals weighted by the weightingprocessing means so that each of the transmission signals from thetransmitting antennas, respectively, becomes a specified value;

matrix product arithmetically operating means for multiplying each ofthe transmission signals which are transmitted from the transmitter by apredetermined matrix, thereby weighting each of the transmissionsignals;

detecting means for detecting whether there is presence or absence of anabnormality in the processing executed by the weighting processing meansor the normalizing means; and

transmitting means for transmitting one of the transmitting signal forwhich the weighting processing means executes the weighting processing,and the transmission signal obtained by the matrix productarithmetically operating means from the transmitter to the receiver inaccordance with the detection result obtained from the detecting means.

In the wireless communication system according to the another embodimentof the present invention, the detecting means detects that an inputsignal beyond a predetermined limit is input to the transmission signalnormalizing means, or that an overflow or an underflow occurs in amiddle of the normalizing processing as an abnormality. In addition, thematrix product arithmetically operating means previously prepares aweighting factor matrix having a row norm guaranteed therefore, andmultiplies each of the transmission signals which are transmitted fromthe transmitter by the weighting factor matrix, thereby weighting eachof the transmission signals. In addition, when the detecting meansdetects the abnormality in the processing, the transmission signalobtained by the matrix product arithmetically operating means istransmitted from the transmitter to the receiver instead of thetransmission signal for which the weighting processing means executesthe weighting processing. As a result, the influence of the arithmeticoperation error or the overflow mixed into each of the transmissionsignals during the normalizing processing is reduced.

According to the embodiments of the present invention, it is possible toprovide the excellent wireless communication system which is capable ofmultiplexing signals and transmitting the multiplexed signals withoutbeing influenced by the crosstalk at all by using the SVD-MIMOcommunication system utilizing the singular value decomposition of thechannel information matrix H, and the apparatus and method for awireless communication.

In addition, according to the embodiments of the present invention, itis possible to provide the excellent wireless communication system whichis capable of realizing the improvement in the transmission speedthrough the SVD-MIMO transmission by reducing the possibility that thetransmission electric power exceeds the upper limit through thesuppression of the fluctuation in row norm of the weighting factormatrix accompanying the arithmetic operation error or the overflow whenthe weighting factor matrix is obtained by using the integerarithmetically operating circuit limited in the word length in thetransmitter, and the apparatus and method for a wireless communication.

Further other objects, features and advantages of the present inventionwill be made clear from a detailed description based on the preferredembodiments which will be described later and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a configuration of awireless communication system according to an embodiment of the presentinvention;

FIG. 2 is a block diagram showing a structural example of a weightingfactor matrix arithmetically operating portion shown in FIG. 1;

FIG. 3 is a block diagram showing another structural example of theweighting factor matrix arithmetically operating portion shown in FIG.1;

FIG. 4 is a block diagram showing a structural example of a terminal inwhich the weighting factor matrix arithmetically operating portion shownin FIG. 1 outputs a weighting factor matrix without carrying outnormalization, and a transmission signal normalizing portion carries outthe normalization for each of transmission signals weighted;

FIG. 5 is a block diagram showing an example of an internal structure ofthe weighting factor matrix arithmetically operating portion shown inFIG. 1 which is applied to the terminal shown in FIG. 4;

FIG. 6 is a block diagram showing another example of the internalstructure of the weighting factor matrix arithmetically operatingportion shown in FIG. 1 which is applied to the terminal shown in FIG.4; and

FIG. 7 is a diagram conceptually showing an SVD-MIMO communicationsystem according to the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 schematically shows a configuration of a wireless communicationsystem according to an embodiment of the present invention. The wirelesscommunication system shown in the figure is composed of a terminal 1 anda terminal 2 each having two antennas, and carries out an MIMOcommunication utilizing space division multiplexing. Here, signaltransmission from the terminal 1 to the terminal 2 is defined now as adown-direction, that is, “downlink”. On the other hand, signaltransmission from the terminal 2 to the terminal 1 is defined now as anup-direction, that is, “uplink”.

Note that, a description will be given below by giving a single carriercommunication as an example. However, of course, the present inventioncan be equally applied to a multi-carrier communication as well typifiedby an orthogonal frequency division multiplexing (OFDM) modulationsystem. In addition, the present invention can also be equally appliedto a communication system as well having an antenna structure other thanthe antenna structure of 2×2 shown in the figure.

In a wireless LAN or the like, normally, a transmission line is usedbetween communication terminals in a time division multiplexing manner.In the time division multiplexing communication, a communication in theup-direction, and a communication in the down-direction are made forapproximately the same period of time. Thus, when the communication inthe up-direction, and the communication in the down-direction are madeat a very short interval of time as compared with a speed at which achannel fluctuates, it is possible to assume that the channel isreversible between the up-direction and the down-direction, that is, asymmetrical property of the channel. In such a case, the followingexpression (7) is established between a channel information matrixH_(up) in the up-direction and a channel information matrix H_(dn) inthe down-direction:H _(up) =H _(dn) ^(T)  (7)

Where a superior T represents transposition of a matrix.

When the SVD-MIMO communication is carried out from the terminal 1toward the terminal 2, the terminal 1 needs to acquire a channelweighting factor matrix V_(dn) in the downlink. A channel informationmatrix estimating portion 11 provided in the terminal 1, for example,obtains a transmission function for each combination of transmitting andreceiving antennas, which is obtained by receiving the known trainingsequences sent from the antennas in a time division manner at theantennas on the terminal 1 side. Also, the channel information matrixestimating portion 11 structures these transmission functions in theform of a matrix in accordance with an arrangement of the antennas,thereby making it possible to estimate the channel information matrixH_(up) in the uplink by utilizing a training period of time.

As shown in the above expression (7), the channel information matrixH_(dn) in the downlink is a transposed matrix (that is, H_(up) ^(T)) ofthe channel information matrix H_(up) in the uplink. Also, a weightingfactor matrix arithmetically operating portion 12 provided in theterminal 1 can obtain the weighting factor matrix V_(dn) by furthersubjecting the channel information matrix H_(dn) to the singular valuedecomposition in the manner as expressed by the following expression(8):H _(dn) =U _(dn) D _(dn) V _(dn) ^(H)  (8)

The weighting factor matrix V_(dn) is obtained in such a manner.Therefore, when the data transmission is carried out from the terminal 1by utilizing the MIMO system, a weighting portion 13 complex-multipliesa transmission signal vector x which is obtained by distributing atransmission signal to the transmitting antennas by the weighting factormatrix V_(dn) as shown in the following expression (9). As a result, theweighting portion 13 obtains transmission signal vectors x′ through thespatial multiplexing, and transmits the resulting transmission signalvectors x′ through the antennas, respectively.x′=V _(dn) x  (9)

In the above description, the MIMO communication system is constructedsuch that the terminal 1 side as a data transmission source calculatesthe weighting factor matrix V_(dn) by utilizing a training signal sentfrom the terminal 2. However, the MIMO communication system can also beconstructed by utilizing any other suitable realizing method. Forexample, the terminal 2 side may be provided with the same channelinformation estimating portion (not shown) as that of the above case. Inthis case, the channel information estimating portion, for example, mayestimate a channel information matrix H_(dn) of the downlink based on atraining sequence received from the terminal 1, and may inform theterminal 1 of the resulting channel information matrix H_(dn) of thedownlink. Or, the terminal 2 side may be further provided with the sameweighting factor matrix arithmetically operating portion as that of theabove case. In this case, the weighting factor matrix arithmeticallyoperating portion may calculate the weighting factor matrix V_(dn) fromthe channel information matrix H_(dn) and may inform the terminal 1 ofthe resulting weighting factor matrix V_(dn). Hereinafter, a descriptionwill be given with respect to the embodiment in which the channelinformation estimating portion and the weighting factor matrixarithmetically operating portion are disposed in the terminal 1 becomingthe sender side for the sake of convenience. However, these functionalmodules may also be disposed in the terminal 2 side becoming thereceiver side.

FIG. 2 shows a structural example of the weighting factor matrixarithmetically operating portion 12 provided in the terminal 1. Here, adescription will now be given with respect to a method of calculatingthe antenna weighting factor matrix V_(dn) in the phase of thetransmission in the downlink in the weighting factor matrixarithmetically operating portion 12 within the terminal 1 by giving, asan example, the case where the MIMO communication system is composed ofthe two transmission antennas and the two reception antennas as shown inFIG. 1.

Firstly, a covariance matrix arithmetically operating portion 121multiples the channel information matrix H_(dn) of the downlink composedof a transposed matrix of the channel information matrix H_(up), of theuplink, estimated by the channel information estimating portion 11 by acomplex conjugate transposed matrix H_(dn) ^(H), thereby calculating acovariance matrix A. Here, the elements of the covariance matrix A aredefined as expressed by the following expression (10):

$\begin{matrix}{A = {\begin{bmatrix}a_{11} & a_{12} \\a_{21} & a_{22}\end{bmatrix} = {H_{dn}^{H}H_{dn}}}} & (10)\end{matrix}$

Here, when λ is an eigenvalue of the covariance matrix A, and v is aneigenvector, relationships shown in the following expressions (11) and(12) are established:Av=λv(A−λI)v=0  (11)det(A−λI)=0  (12)

where det represents a determination of a matrix. Also, a quadraticequation (13) which will be shown below can be obtained from the aboveexpressions (10) and (12):(a ₁₁−λ)(a ₂₂−λ)−a ₁₂ a ₂₁=0 λ²(a ₁₁ +a ₂₂)λ+(a ₁₁ a ₂₂ −a ₁₂ a₂₁)=0  (13)

An eigenvalue arithmetically operating portion 122 solves this quadraticequation (13) to obtain eigenvalues λ₁ and λ₂ of the covariance matrixA. As previously stated, D_(dn) is a diagonal matrix which has squareroots of these eigenvalues λ₁ and λ₂ in a diagonal term.

Subsequently, an eigenvector arithmetically operating portion 123substitutes these eigenvalues λ₁ and λ₂ into the above expression (11)to obtain eigenvectors. A large number of combinations exist as theeigenvectors obtained here. One of the eigenvectors is expressed by thefollowing expression (14):

$\begin{matrix}{\left\lbrack {v_{1},v_{2}} \right\rbrack = \begin{bmatrix}a_{12} & {\lambda_{2} - a_{22}} \\{\lambda_{1} - a_{11}} & a_{21}\end{bmatrix}} & (14)\end{matrix}$

A normalizing portion 124 normalizes this combination of theeigenvectors to obtain the weighting factor matrix V_(dn). The reasonfor carrying out the normalization is because a matrix which isnormalized so that a row norm is normalized to 1 is used as theweighting factor matrix in the weighting portion 13 in a subsequentstage, thereby preventing the transmission output from fluctuating(exceeding the upper limit) for any weighting factor matrix. Theweighting factor matrix V_(dn) is expressed by either the followingexpression (15) or (16):

$\begin{matrix}{V_{dn} = \begin{bmatrix}{a_{12}/s_{1}} & {\left( {\lambda_{2} - a_{22}} \right)/s_{2}} \\{\left( {\lambda_{1} - a_{11}} \right)/s_{1}} & {a_{21}/s_{2}}\end{bmatrix}} & (15)\end{matrix}$

where s₁=√{square root over (a₁₂ ²+(λ₁−a₁₁)²)}, and s₂=√{square rootover ((λ₂−a₂₂)²+a₂₁ ²)}.

$\begin{matrix}{V_{dn} = \begin{bmatrix}{a_{12}/t_{1}} & {\left( {\lambda_{2} - a_{22}} \right)/t_{1}} \\{\left( {\lambda_{1} - a_{11}} \right)/t_{2}} & {a_{21}/t_{2}}\end{bmatrix}} & (16)\end{matrix}$

where t₁=√{square root over (a₁₂ ²+(λ₂−a₂₂)²)}, and t₂=√{square rootover ((λ₁−a₁₁)²+a₂₁ ²)}.

The weighting portion 13 in the subsequent stage weights each of thetransmission signal vectors x based on the weighting factor matrixV_(dn) stated above.

An integer arithmetic operation is carried out on the actual equipmentfrom the necessity for executing real-time processing for calculation ofthe antenna weighting factor matrix V_(dn) as described above by usingan arithmetic operation circuit which is structured in realistic circuitscale. Unlike the actual number arithmetic operation, the integerarithmetic operation causes the increase in arithmetic operation error,the overflow or the underflow due to the influence of the limitation inthe word length. This leads to that there is the high possibility thatthe row norm of the weighting factor matrix V_(dn) largely fluctuates.As a result, there is the dangerousness that the weighting factor matrixprovides the unexpected value, and thus the transmission output exceedsthe upper limit controlled by the Radio Law in the terminal 1.

On the other hand, in this embodiment, as shown in FIG. 2, thenormalization is carried out in the final stage in the weighting factormatrix arithmetically operating portion 12. Thereby, the fluctuation inthe row norm of the weighting factor matrix V_(dn) is effectivelysuppressed. If the arithmetic operation error or the like is mixed intothe transmission signals in the arithmetic operation before thenormalization, the row norm of the output weighting factor matrix V_(dn)gets usually a constant value as long as the normalizing portion 124properly carries out the normalizing operation.

The following method, for example, can be given as an alternative of themethod of normalizing the weighting factor matrix V_(dn) in the finalstage in the weighting factor matrix arithmetic operating portion 12 asdescribed above. That is to say, the singular value decomposition can becarried out for the channel information matrix H_(UP) of the uplink(H_(UP)=U_(UP)D_(UP)V_(UP) ^(H)) to obtain and D_(UP) and V_(UP)similarly to the above case (V_(UP) is normalized in the final stage).Also, the transmitting antenna weighting factor matrix V_(dn) in thephase of the downlink can be obtained from a relationship represented bythe following expression (17):V _(dn) =U _(UP)*=(H _(UP) V _(UP) D _(up) ⁻¹)*  (17)

where * represents the complex conjugate, and ⁻¹ represents an inversematrix.

In this case, the arithmetic operation is further carried out aftercompletion of the normalization, which increases the possibility thatthe fluctuation of the row norm of the transmitting antenna weightingfactor matrix V_(dn) occurs due to the arithmetic operation error.

Consequently, as shown in FIG. 2, the weighting factor arithmeticallyoperating portion 12 normalizes the weighting factor matrix V_(dn) inthe final stage therein, thereby making it possible to suppress thefluctuation in row norm of the output weighting factor matrix V_(dn).

Until now, the description has been given on the assumption that the rownorm of the output weighting factor matrix V_(dn) is usually held at theconstant value as long as the normalizing portion 124 properly carriesout the normalizing operation. However, the proper operation of theweighting factor arithmetically operating portion 12 is not necessarilyguaranteed in the integer arithmetic operation limited in the wordlength. For example, in the case where the input signal to the weightingfactor matrix arithmetically operating portion 12 exceeds the unexpectedlimit, it is possible that the arithmetic operation error occurs, or theoverflow or the underflow occurs in the middle of the arithmeticoperation. In particular, the normalizing portion 124 in the final stageof the weighting factor matrix arithmetically operating portion 12carries out the division based on the square-root of sum of squares(refer to the above expressions (15) and (16)). As a result, there isthe high possibility that the arithmetic operation error for the toolarge input or the too small input becomes large.

From the above, in this embodiment, in order to cope with such a problemas well, the weighting factor matrix arithmetically operating portion 12includes a detector 126 for detecting occurrence of abnormal situationswhich will be described below:

(1) The input signal to the normalizing portion 124 is beyond theexpected limit (too large or too small).

(2) The overflow or the underflow occurs in the middle of the arithmeticoperation for normalization.

When the detector 126 detects these situations, the row norm of theoutput weighting factor matrix is largely different from the expectedvalue. As a result, there is the high possibility that the transmissionelectric power becomes beyond the upper limit set by the Radio Lawcontrol. For this reason, a default weighting factor matrix which ispreviously stored in a read only memory (ROM) 125 is output to theweighting portion 13 in the subsequent stage through a switch 127instead of the arithmetic operation result obtained from the normalizingportion 124 in accordance with a detection output from the detector 126.

Here, the normalized weighting factor matrix is prepared in the ROM 125,so that the row norm gets the expected value. In addition, the unitmatrix, the rotation matrix having the suitable angle, the mirrormatrix, the Walsh-Hadamard matrix, the matrix obtained by combiningthese two or more matrices with each other or the like, for example, canbe used as the weighting factor matrix previously stored in the ROM 125.

In addition, a plurality of different weighting factor matrices may beprepared in the ROM 125. In this case, when the detector 126 detects theabnormality in the processing based on the input signal to thenormalizing portion 124, the result in the arithmetic operation or thelike, the weighting factor matrix arithmetically operating portion 12may suitably select one, which is expected to be most suitable, fromamong the plurality of different weighting factor matrices prepared inthe ROM 125. Also, the weighting factor matrix arithmetically operatingportion 12 may output the weighting factor matrix thus selected insteadof the result of the arithmetic operation carried out in the normalizingportion 124. For example, a plurality of rotation matrices having therespective angles may be previously prepared in the ROM 125. In thiscase, the weighting factor matrix arithmetically operating portion 12may select one having the angle nearest the weighting factor matrixbefore the normalization is carried out from among the plurality ofrotation matrices having the respective angles.

FIG. 3 shows another structural example of the weighting factor matrixarithmetically operating portion 12. It is as previously described thatwhen the eigenvalues λ₁ and λ₂ calculated by the eigenvaluearithmetically operating portion 122 are substituted into the aboveexpression (11), a large number of combinations exist in terms of theeigenvector. In the another structural example of the weighting factormatrix arithmetically operating portion 12 shown in FIG. 3, theeigenvector arithmetically operating portion 123 produces a pluralityset of eigenvectors obtained by arithmetically operating the eigenvaluesλ₁ and λ₂. Also, the eigenvector arithmetically operating portion 123selects suitable one from among the plurality set of eigenvectorsthrough a switch 128, and outputs the set of eigenvectors thus selectedto the subsequent normalizing portion 124.

“The matrix having the low possibility that the arithmetic operationerror finally occurs”, for example, can be given as the selectioncriteria in accordance with which the suitable one is selected fromamong a plurality set of eigenvectors through the switch 128.

Although the above expression (14) has already been given as one of theexpressions each representing the eigenvectors, the following expression(18) is also given as one of the expressions each representing theeigenvectors:

$\begin{matrix}{\left\lbrack {v_{1},v_{2}} \right\rbrack = \begin{bmatrix}{\lambda_{1} - a_{22}} & a_{12} \\a_{21} & {\lambda_{2} - a_{11}}\end{bmatrix}} & (18)\end{matrix}$

When the normalizing portion 124 normalizes the eigenvectors representedby the above expression (18), the weighting factor matrix V_(dn)expressed by the following expression (19) or (20) can be obtainedsimilarly to the above case.

$\begin{matrix}{V_{dn} = \begin{bmatrix}{\left( {\lambda_{1} - a_{22}} \right)/s_{1}} & {a_{12}/s_{2}} \\{a_{21}/s_{1}} & {\left( {\lambda_{2} - a_{11}} \right)/s_{2}}\end{bmatrix}} & (19)\end{matrix}$

where s₁=√{square root over ((λ₁−a₂₂)²+a₂₁ ²)}, and s₂=√{square rootover (a₁₂ ²+(λ₂−a₁₁)²)}.

$\begin{matrix}{V_{dn} = \begin{bmatrix}{\left( {\lambda_{1} - a_{22}} \right)/t_{1}} & {a_{12}/t_{1}} \\{a_{21}/t_{2}} & {\left( {\lambda_{2} - a_{11}} \right)/t_{2}}\end{bmatrix}} & (20)\end{matrix}$

where t₁=√{square root over ((λ₁−a₂₂)²+a₁₂ ²)}, and t₂=√{square rootover (a₂₁ ²+(λ₂−a₁₁)²)}.

Here, let us consider such a case where the channel information matrix His degenerated. In this case, since the eigenvalue λ₂ becomes zero, theabove expressions (14) and (18) can be transformed into the followingexpressions (21) and (22), respectively:

$\begin{matrix}{\left\lbrack {v_{1},v_{2}} \right\rbrack = \begin{bmatrix}a_{12} & {- a_{22}} \\{\lambda_{1} - a_{11}} & a_{21}\end{bmatrix}} & (21) \\{\left\lbrack {v_{1},v_{2}} \right\rbrack = \begin{bmatrix}{\lambda_{1} - a_{22}} & a_{12} \\a_{21} & {- a_{11}}\end{bmatrix}} & (22)\end{matrix}$

At this time, in such a case where an element a₂₂ contained in thecovariance matrix is close to zero, there is the high possibility thatan element s₂ in the above expression (15) or an element t₁ in the aboveexpression (16) becomes close to zero. When a denominator becomes closeto zero, an error in an arithmetic operation of division for an integralnumber generally becomes large. For this reason, in this case, thepossibility that the arithmetic operation finally contains therein theerror becomes higher in carrying out the arithmetic operation fornormalizing the weighting factor matrix V_(dn) from the eigenvectorsexpressed by the expression (21) than in carrying out the arithmeticoperation for normalizing the weighting factor matrix V_(dn) from theeigenvectors expressed by the expression (22).

On the other hand, in such a case where an element a₁₁ contained in thecovariance matrix is close to zero, there is the high possibility thatan element s₂ in the above expression (19), or an element t₂ in theabove expression (21) becomes close to zero. For this reason, in thiscase, the possibility that the arithmetic operation finally containstherein the error becomes higher in carrying out the arithmeticoperation for normalizing the weighting factor matrix V_(dn) from theeigenvectors expressed by the expression (22) than in carrying out thearithmetic operation for normalizing the weighting factor matrix V_(dn)from the eigenvectors expressed by the expression (21).

Therefore, under such a communication environment that the channelinformation matrix H is degenerated, the following switching control iscarried out by using the switch 128 in accordance with the selectioncriteria with which “the matrix having the low possibility that thearithmetic operation error finally occurs” is selected from among aplurality of eigenvectors, thereby making it possible to reduce thenumber of arithmetic operation errors.

(1) When a₁₁>a₂₂, or a₁₁≧a₂₂, a set of eigenvectors expressed by theabove expression (18) is selected, and is supplied to the normalizingportion 124.

(2) a₁₁≦a₂₂, or a₁₁<a₂₂, a set of eigenvectors expressed by the aboveexpression (14) is selected, and is supplied to the normalizing portion124.

It has been described until now that the weighting factor matrixarithmetically operating portion 12 carries out the normalization.However, such a structure as shown in FIG. 4 can also be adopted. Thatis to say, the weighting factor matrix arithmetically operating portion12 carries out no normalization, and outputs the weighting factormatrix. Also, the transmission signal normalizing portion 18 (disposedoutside the weighting factor matrix arithmetically operating portion 12)normalizes each of the weighted transmission signals.

In the structural example of the weighting factor matrix arithmeticallyoperating portion 12 shown in FIG. 2, the normalizing processing isexecuted in the final stage in the weighting factor matrixarithmetically operating portion 12. As a result, the influence of thearithmetic operation error or the overflow when the weighting factormatrix is calculated based on the integer arithmetic operation isreduced, thereby effectively suppressing the fluctuation in row norm ofthe weighting factor matrix V_(dn). On the other hand, in the anotherstructural example of the weighting factor matrix arithmeticallyoperating portion 12 shown in FIG. 4, the transmission signalnormalizing portion 18 executes the normalizing processing after each ofthe transmission signal vectors x is weighted with the eigenvectors.Likewise, the influence of the arithmetic operation error or theoverflow can be reduced, thereby effectively suppressing the fluctuationin row norm of the weighting factor matrix V_(dn).

The weighting factor matrix arithmetically operating portion 12 shown inFIG. 4, for example, has a structure as shown in FIG. 5 or 6.

In the structural example shown in FIG. 5, in the weighting factormatrix arithmetically operating portion 12, the covariance matrixarithmetically operating portion 121 calculates the covariance matrix Afrom the channel information matrix of the downlink. The eigenvaluearithmetically operating portion 122 obtains the eigenvalues of thecovariance matrix A. Also, the eigenvector arithmetically operatingportion 123 arithmetically operates the eigenvectors, and outputs theresulting eigenvectors.

A large number of combinations exist in terms of the eigenvectors (thisis previously stated). In the structural example shown in FIG. 6, aplurality set of eigenvectors which are obtained by arithmeticallyoperating the eigenvectors λ₁ and λ₂ are prepared. Suitable one isselected from among the plurality set of eigenvectors through a switch128, and is output to the subsequent weighting portion 13. “The matrixhaving the low possibility that the arithmetic operation error finallyoccurs”, for example, can be given as the selection criteria inaccordance with which suitable one is selected from among the pluralityset of eigenvectors through the switch 128 (the same as the above).

When the weighting factor matrix arithmetically operating portion 12shown in FIG. 5 or 6 outputs the weighting factor matrix V_(dn), thesubsequent weighting portion 13 executes the weighting processing bycomplex-multiplexing each of the transmission signal vectors x by theweighting factor matrix V_(dn). Here, each of the transmission signalvectors x is obtained by distributing the transmission data to thetransmitting antennas. Subsequently, after each of the transmissionsignals is weighted with the weighting factor matrix V_(dn), thetransmission signal normalizing portion 18 executes the processing fornormalizing each of the transmission signals.

When the transmission signal normalizing portion 18 properly executesthe normalizing processing, the norm of each of the output transmissionvectors is usually held at the constant value. However, the properoperation is not necessarily guaranteed for the processing in thetransmission signal normalizing portion 18. The reason for this isbecause it is possible that the division or the like based on thesquare-root of sum of squares is contained in the normalizingprocessing, and thus when such normalizing processing is executed basedon the integer arithmetic operation limited in the word length, theinput signal becomes beyond the expected limit, so that the arithmeticoperation error occurs, and the overflow or the underflow occurs in themiddle of the arithmetic operation.

Thus, the detector 15 is provided with a function of detectingoccurrence of the following abnormal situations.

(1) The input signal to the transmission signal normalizing portion 18is beyond the expected limit (too large or too small).

(2) The overflow or the underflow occurs in the middle of the arithmeticoperation for normalization by the transmission signal normalizingportion 18.

When the detector 15 detects these situations, the row norm of theoutput weighting factor matrix is largely different from the expectedvalue. As a result, there is the high possibility that the transmissionelectric power becomes beyond the upper limit set by the Radio Lawcontrol. For this reason, a matrix product obtained by multiplying eachof the transmission signal vector x by the predetermined matrix in amatrix product arithmetic operating portion 17 is selected through theswitch 16 instead of the arithmetic operation result obtained in thetransmission signal normalizing portion 18 in accordance with thedetection output from the detector 15. Also, the elements of theresulting matrix product are sent out through the transmitting antennas,respectively. Here, the matrix product arithmetically operating portion17 previously stores the weighting factor matrix, having the row normguaranteed therefore, such as the unit matrix, the rotation matrixhaving the suitable angle, the mirror matrix, the Walsh-Hadamard matrix,or the matrix obtained by combining these two or more matrices with eachother in the ROM or the like. In this case, none of the transmissionsignal vectors x is weighted with the weighting factor matrix having therow norm becoming the unexpectedly large value. As a result, thepossibility that the transmission electric power becomes beyond theupper limit set by the Radio Law control becomes very low.

It is noted that in the structural example of the terminal 1 shown inFIG. 4, either the normalized weighting factor matrix may be previouslyprepared in the matrix product arithmetically operating portion 17, orthe normalizing processing may be executed after each of thetransmission signals is weighted.

In addition, in the circuit structure as well of the terminal 1 shown inFIG. 4, the weighting factor matrix is previously stored in a ROM (notshown). In this case, it is detected that the problem about the increasein arithmetical operation error, or the overflow or the underflow due tothe influence of the limit in the word length is caused. Also, theweighting factor matrix of the default is output from the ROM to theweighting portion 13 in the subsequent stage instead of the arithmeticoperation result obtained from the transmission signal normalizingportion 18. As a result, the row norm of the weighting factor matrix canbe prevented from unexpectedly fluctuating. Here, the unit matrix, therotation matrix having the suitable angle, the mirror matrix, theWalsh-Hadamard matrix, the matrix obtained by combining these two ormore matrices with each other, or the like, for example, can be used asthe weighting factor matrix which is previously stored in the ROM.

The present invention has been described in detail so far whilereference is made to the specific embodiment. However, it is obviousthat modifications and substitutions of the embodiment concerned can bemade by those skilled in the art without departing from the gist of thepresent invention. That is to say, the present invention has beendisclosed merely in the form of an exemplification, and thus thecontents of the description of this specification should not be intendedto be construed in a limiting sense. In order to determine the gist ofthe present invention, the appended claims should be taken intoconsideration.

What is claimed is:
 1. A wireless communication system for carrying outa spatial multiplexing communication between a transmitter having aplurality of antennas, and a receiver having a plurality of antennas,the wireless communication system comprising: channel information matrixacquiring means for acquiring a channel information matrix havingtransmission functions of the pairs of antennas between the sender sideand the receiver side as elements; weighting factor matrixarithmetically operating means for obtaining a weighting factor matrixbased on the channel information matrix thus acquired; weightingprocessing means for executing weighting processing based on theweighting factor matrix for transmission signals which are transmittedfrom the transmitter; transmission signal normalizing means forexecuting processing for normalizing each of the transmission signalsweighted by the weighting processing means so that each of electricpowers of the transmission signals from the respective transmittingantennas becomes a specified value; matrix product arithmeticallyoperating means for multiplying each of the transmission signals whichare transmitted from the transmitter by a predetermined matrix, therebyweighting each of the transmission signals; detecting means fordetecting whether there is presence or absence of an abnormality in theprocessing executed by the weighting processing means or the normalizingmeans; and transmitting means for transmitting one of the transmittingsignal for which the weighting processing means executes the weightingprocessing, and the transmission signal obtained by the matrix productarithmetically operating means from the transmitter to the receiver inaccordance with the detection result obtained from the detecting means.2. The wireless communication system according to claim 1, wherein thedetecting means detects that an input signal beyond a predeterminedlimit is input to the transmission signal normalizing means, or that anoverflow or an underflow occurs in a middle of the arithmetic operationfor the normalization as abnormality.
 3. The wireless communicationsystem according to claim 1, wherein the matrix product arithmeticallyoperating means previously prepares a weighting factor matrix having arow norm guaranteed therefore, and multiplies each of the transmissionsignals which are transmitted from the transmitter by the weightingfactor matrix to weight each of the transmission signals.
 4. Thewireless communication system according to claim 3, wherein the matrixproduct arithmetically operating means previously prepares a unitmatrix, a rotation matrix having a suitable angle, a mirror matrix, aWalsh-Hadamard matrix, or a matrix obtained by combining these two ormore matrices with each other.
 5. A wireless communication apparatusincluding a plurality of antennas for carrying out a spatialmultiplexing communication with a receiver having a plurality ofantennas, the wireless communication apparatus comprising: weightingfactor matrix arithmetically operating means for obtaining a weightingfactor matrix based on a channel information matrix having transmissionfunctions of the pairs of antennas between the sender side and thereceiver side as elements; weighting processing means for executingweighting processing, based on the weighting factor matrix, fortransmission signals which are transmitted through the antennas,respectively; transmission signal normalizing means for executingprocessing for normalizing each of the transmission signals weighted bythe weighting processing means so that each of electric powers of thetransmission signals from the respective transmitting antennas becomes aspecified value; matrix product arithmetically operating means formultiplying each of the transmission signals which are transmittedthrough the antennas, respectively, by a predetermined matrix, therebyweighting each of the transmission signals concerned; detecting meansfor detecting whether there is presence or absence of an abnormality inthe processing executed by the weighting processing means or thenormalizing section; and transmitting means for transmitting one of thetransmitting signal for which the weighting processing means executesthe weighting processing, and the transmission signal obtained by thematrix product arithmetically operating means from the transmitter tothe receiver in accordance with the detection result obtained from thedetecting means.
 6. The wireless communication apparatus according toclaim 5, wherein the detecting means detects that an input signal beyonda predetermined limit is input to the transmission signal normalizingmeans, or that an overflow or an underflow occurs in a middle of thearithmetic operation for the normalization as abnormality.
 7. Thewireless communication apparatus according to claim 5, wherein thematrix product arithmetically operating means previously prepares aweighting factor matrix having a row norm guaranteed therefore, andmultiplies each of the transmission signals which are transmitted fromthe transmitter by the weighting factor matrix to weight each of thetransmission signals.
 8. The wireless communication apparatus accordingto claim 7, wherein the matrix product arithmetically operating meanspreviously prepares a unit matrix, a rotation matrix having a suitableangle, a mirror matrix, a Walsh-Hadamard matrix, or a matrix obtained bycombining these two or more matrices with each other.
 9. A wirelesscommunication method of carrying out a spatial multiplexingcommunication with a receiver having a plurality of antennas by using aplurality of antennas, the wireless communication method comprising thesteps of: arithmetically operating a weighting factor matrix based on achannel information matrix having transmission functions of the pairs ofantennas between the sender side and the receiver side as elements;executing weighting processing, based on the weighting factor matrix,for each of transmission signals which are transmitted through theantennas, respectively; executing processing for normalizing each of thetransmission signals weighted in the weighting processing so that eachof electric powers of the transmission signals which are transmittedthrough the transmission antennas, respectively, becomes a specifiedvalue; multiplexing each of the transmission signals which aretransmitted through the antennas, respectively, by a predeterminedmatrix, thereby weighting each of the transmission signals; detectingwhether there is presence or absence of an abnormality in the processingexecuted in the weighting processing step or in the normalizing step;and transmitting one of the transmission signal for which the weightingprocessing is executed in the weighting processing step, and thetransmission signal obtained in the matrix product arithmeticallyoperating step in accordance with a detection result obtained in thedetecting step.
 10. The wireless communication method according to claim9, wherein in the detecting step, it is detected as an abnormality inthe processing that an input signal beyond a predetermined limit isinput to the transmission signal normalizing step, or that an overflowor an underflow occurs in a middle of the arithmetic operation for thenormalization.
 11. The wireless communication method according to claim9, wherein in the matrix product arithmetically operating step, each ofthe transmission signals which are transmitted through the antennas,respectively, is weighted with a weighting factor matrix having a rownorm guaranteed therefore.
 12. The wireless communication methodaccording to claim 11, wherein in the matrix product arithmeticallyoperating step, a unit matrix, a rotation matrix having a suitableangle, a mirror matrix, a Walsh-Hadamard matrix, or a matrix obtained bycombining these two or more matrices with each other is used.
 13. Awireless communication system for carrying out a spatial multiplexingcommunication between a transmitter having a plurality of antennas, anda receiver having a plurality of antennas, the wireless communicationsystem comprising: a channel information matrix acquiring sectionconfigured to acquire a channel information matrix having transmissionfunctions of the pairs of antennas between the sender side and thereceiver side as elements; a weighting factor matrix arithmeticallyoperating section configured to obtain a weighting factor matrix basedon the channel information matrix thus acquired; a weighting processingsection configured to execute weighting processing based on theweighting factor matrix for transmission signals which are transmittedfrom the transmitter; a transmission signal normalizing sectionconfigured to execute processing for normalizing each of thetransmission signals weighted by the weighting processing section sothat each of electric powers of the transmission signals from therespective transmitting antennas becomes a specified value; a matrixproduct arithmetically operating section configured to multiply each ofthe transmission signals which are transmitted from the transmitter by apredetermined matrix, thereby weighting each of the transmissionsignals; a detecting section configured to detect whether there ispresence or absence of an abnormality in the processing executed by theweighting processing section or the normalizing section; and atransmitting section configured to transmit one of the transmittingsignal for which the weighting processing section executes the weightingprocessing, and the transmission signal obtained by the matrix productarithmetically operating section from the transmitter to the receiver inaccordance with the detection result obtained from the detectingsection.
 14. A wireless communication apparatus including a plurality ofantennas for carrying out a spatial multiplexing communication with areceiver having a plurality of antennas, the wireless communicationapparatus comprising: a weighting factor matrix arithmetically operatingsection configured to obtain a weighting factor matrix based on achannel information matrix having transmission functions of the pairs ofantennas between the sender side and the receiver side as elements; aweighting processing section configured to execute weighting processing,based on the weighting factor matrix, for transmission signals which aretransmitted through the antennas, respectively; a transmission signalnormalizing section configured to executing processing for normalizingeach of the transmission signals weighted by the weighting processingsection so that each of electric powers of the transmission signals fromthe respective transmitting antennas becomes a specified value; a matrixproduct arithmetically operating section configured to multiply each ofthe transmission signals which are transmitted through the antennas,respectively, by a predetermined matrix, thereby weighting each of thetransmission signals concerned; a detecting section configured to detectwhether there is presence or absence of an abnormality in the processingexecuted by the weighting processing section or the normalizing section;and a transmitting section configured to transmit one of thetransmitting signal for which the weighting processing section executesthe weighting processing, and the transmission signal obtained by thematrix product arithmetically operating section from the transmitter tothe receiver in accordance with the detection result obtained from thedetecting section.